Switchable lever for a valve drive of an internal combustion engine

ABSTRACT

A switchable lever for a valve drive of an internal combustion engine which has two side walls with ends connected by a crossbar. There is a gas-exchange valve system in the crossbar at one end and a bearing for the pivotable support of the crossbar at the other end. An axle is held nondisplaceably in the side walls, between the ends, with two cam rollers running on the axle. The cam rollers are displaceable axially on the axle toward each other into a first position such that the cam rollers run up to each other on a longitudinal center plane of the lever and away from each other into a second position. One of the positions serves for a high-lift cam contact and the other position serves for a low-lift or zero-lift cam contact.

CROSS-REFERENCE TO RELATED APPLICATION

This application is claims the priority of DE 10 2010 019 065.9 filed May 3, 2010, which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a switchable lever for a valve drive of an internal combustion engine.

BACKGROUND OF THE INVENTION

The lever revealed in subsequently published DE 102010011828.1 is considered to be the closest prior art. It is noticeable that the axle has to be acted upon in a complicated manner via external means in order to be displaced. In association therewith, the abovementioned lever requires a relatively large amount of construction space laterally, and, at least in the switching state shown in FIG. 5, an asymmetrical introduction of force occurs during the cam lift. It is also ascertained that the central region of the lever has a relatively large bulge because of the displaceable cam rollers positioned next to one another on the axle.

It is therefore the object of the invention to develop the lever of the type mentioned at the beginning to the effect that said lever no longer has the disadvantages described.

SUMMARY OF THE INVENTION

The invention is directed to a switchable lever for a valve drive of an internal combustion engine, which has two side walls with ends that are connected by a crossbar. A gas-exchange valve system is present in the crossbar at one end and a bearing for the pivotable support of the crossbar is present at the other end. An axle is held in the side walls between the ends with two cam rollers running on the axle. The cam rollers are displaceable relative to each other into a first position via a first servo means and are displaceable away relative from each other into a second position via a second servo means. One of the positions serves for a high-lift cam contact [switching to a large valve lift] and the other of the positions serves for a low-lift or zero-lift cam contact [switching to a low or 0 valve lift].

More specifically, the object is achieved in that the axle is held axially nondisplaceably in the side walls. The cam rollers can be displaced toward each other into a first position via a first servo means such that the cam rollers abut each other on a longitudinal center plane of the lever and the cam rollers can be displaced in the same manner away from each other into a second position via a second servo means.

A lever is therefore present without the disadvantages referred to at the beginning. A particularly outstanding feature of the invention is the ultimately telescopic nesting of the cam rollers together with the support rollers, thus making it possible to save on construction space laterally. At the same time, forces are introduced into the lever symmetrically during the cam lift such that the lever has only an insignificant tilting tendency, if any at all. The cam rollers can be physically broad such that the loading on the components by the surface pressure is minimized. In addition, simple internal actuating means are proposed for the cam rollers for the displacement thereof (hydraulic medium/compression spring), and separate pressure spaces for the hydraulic medium can be omitted owing to said pressure spaces being formed axially between the support and cam rollers. It is obvious that this simultaneously provides excellent lubrication of the sealing rotary tapping between the inner annular casing of the particular cam roller and an outer casing of the support roller.

Hydraulic actuation of the cam rollers on both sides is optionally also possible. Alternative actuating means for displacing the cam rollers counter to the pressure of hydraulic medium, such as magnetic or electromagnetic means etc., are also conceivable.

The support rollers proposed in a development of the invention are expediently directly adjacent to the side walls of the lever. Said support rollers may be, but do not have to be, rotatable in relation to the axle. According to the invention, the cam rollers are supported in both the positions thereof on the support rollers such that, during a cam lift, force is simultaneously introduced via the cam and support rollers. Hydraulic medium from the circuit of the internal combustion engine is preferred as the servo means for producing the first position. However, brake fluid or a separate hydraulic medium circuit may also be used.

At least one co-rotating helical compression spring clamped between the cam rollers is proposed as the spring means for producing the second position. Said helical compression spring expediently sits in annular pockets of the inner faces of the cam rollers. It is advantageous here to place said annular pockets radially higher than the support rollers, thus providing sufficient construction depth for the latter.

A further embodiment relates to measures for supplying the hydraulic medium to the pressure space. It has proven particularly expedient to introduce the hydraulic medium for the lever from the bearing, which bearing can be designed as a dome for a head of a supporting element. Hydraulic medium is conducted in a simple manner via, for example, drilled transverse and longitudinal channels and a rotary tapping on the axle into the axle and from there to the pressure spaces. If the lever is not to be produced from steel sheet by punching and bending, but rather, for example, is to be cast, the channels may also be cast therein at the same time. It is also conceivable for the transverse and longitudinal channels to be formed separately and retrospectively arranged on the outer casing of the lever.

According to another expedient physical embodiment of the invention, a center stop for the cam rollers runs on the axle. Said center stop can be designed as a simple snap ring or the like sitting in an annular groove. As an alternative, an annular collar on the axle is also possible.

A sliding mounting for the cam rollers on the axle is preferred, with a needle-type mounting also being possible. Should support rollers be used, the same applies thereto.

Primarily, but not exclusively, either a rocker arm lever which can be mounted on a supporting element, or an oscillating lever which can be arranged on an oscillating axis, are possible as the cam-following lever. Given a sufficient amount of construction space, the roller sliding system proposed may also be used on a tilting lever or roller tappet.

Owing to the optionally provided support surfaces, for example on upper sides of the side walls, the lever can be supported as it passes through the cam base circle such that the respective cam base circles are free from contact with the cam rollers, which minimizes the effort expended on displacing the latter. Possible mating support surfaces include, for example, support cams on the earn shaft or elements which protrude from the cylinder head and project beyond the side walls.

A further contribution to reducing the component costs is made if, as proposed, the two support rollers are identical to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained with reference to the drawing, in which:

FIG. 1 shows a spatial view of a lever according to the invention;

FIG. 2 shows a top view according to FIG. 1;

FIG. 3 shows a cross section through the lever in the region of the axle with the cam rollers in a first position (low cam lift); and

FIG. 4 shows the cross section as previously, but with the cam rollers in the second position (large cam lift).

DETAILED DESCRIPTION OF THE INVENTION

A switchable lever 1 in the form of a rocker arm lever for a valve drive of an internal combustion engine is illustrated. Said lever has a box-shaped geometry in top view and consists of two upright side walls 2, the ends 3, 4 of which are connected on their lower side by a cross bar 5. The side walls 2 have an expanded center section 30 which is adjoined by intermediate sections 31 which face each other and peter out in rectilinear end sections 32.

There is a gas-exchange valve system 6 in the crossbar 5 at the one end 3 and a bearing 7, which is designed as a dome-shaped formation and is intended for the pivotable supporting of the lever 1, at the other end 4. An axle 8 is held nondisplaceably in the side walls 2 between the ends 3, 4. Two axially displaceable cam rollers 9 run slideably on said axle.

FIG. 3 shows a first position of the cam rollers 9, in which said cam rollers run up to each other on a longitudinal center plane of the lever 1. For the correct center alignment of said cam rollers, a snap ring on the axle 8 is shown in the form of a stop element 29. This position serves for a low-lift cam contact [switching to a low valve lift].

FIG. 4 shows a second position of the cam rollers 9, in which said cam rollers are displaced away from each other. This position serves for a high-lift can contact [switching to a high valve lift].

A pair of diametrically opposite support rollers 12 of smaller outside diameter than the cam rollers 9 is added, fixed axially, to the axle 8, adjacent to the side walls 2 (see FIGS. 3, 4). The outer faces 13 of the cam rollers 9 each have a cylindrical pocket 14, via the inner annular casing 15 of which said cam rollers are mounted “in a sucking manner” on an outer casing 16 of the particular support roller 12 in both positions.

A pressure space 19 for hydraulic medium, which can be introduced via the axle 8, is produced axially between a base 17 of the respective pocket 14 and an inner face 18 of the adjacent slideably mounted support roller 16 as a first servo means 10 (sec FIG. 3). At the same time, a mechanical spring means present in the form of a helical compression spring is clamped between the inner faces 20 of the cam rollers 9 as a second servo means 11. It can be seen that opposite annular pockets 21 run on the inner faces 20 of the cam rollers 9, the spring means 11 sitting in said annular pockets and the end sides of said spring means being supported on the bottoms 22 of the said pockets. The annular pockets 21 run in a radial region above the support rollers 12, and therefore there is sufficient construction space.

In order to produce the first position, the cam rollers 9 can be displaced towards each other, counter to the force of the spring means 11, by high pressure at the hydraulic medium 10, which can be conducted into the pressure space 19. In order to produce the second position, the cam rollers 9, with the high pressure at the hydraulic medium 10 switched off, can be displaced away from each other by the force of the spring means 11.

As is revealed in more detail in FIG. 2, the hydraulic medium 10 is introduced via a supply line 23 in the lever 1. The supply line 23 starts from the bearing 7 at the other end 4 and is fed via a head of a supporting element, on which the lever 1 lies together with the bearing 7 thereof when installed. The supply line 23 consists of a transverse channel 24 in the crossbar 5, which channel opens at an outer end into a longitudinal channel 25 of the respective side wall 2, which longitudinal channel 25 communicates with an annular-groove/bore overflow 26 in the axle 8. The supply line 23 is conducted further from said overflow to an axial channel 27 in the axle 8. One radial passage 28 branches off from the axial channel 27 per pressure space 19, the radial passage being positioned axially close to the inner face 18 of the corresponding support roller 12.

It can also be gathered from FIG. 1 that upper sides 33 of the side walls 2 have support surfaces 34. Via said support surfaces, the lever 1 can be supported, as it passes through the cam base circle, on support cams of the cam shaft, which is located thereabove upon installation, in such a manner that the cam rollers 9 of said lever, as they pass through the cam base circle, run with play with respect to the base circle of the counter running cams and can therefore be displaced relatively easily.

If, when passing through the cam base circle, the lever 1 is to be switched over to a low cam lift (low-lift cam running centrally thereabove), then, as FIG. 3 shows, the pressure space 19 is flooded with hydraulic medium 10, and therefore the cam rollers 9 are moved toward each other and come into contact with each other by the inner faces 20 thereof. The high-lift cams located on both sides of the central low-lift cam are then not in engagement (first position).

In order to switch back (second position), during the running through the cam base circle, the high pressure at the hydraulic medium 10 in the pressure space 19 is reduced such that the co-rotating spring means 11 presses the cam rollers 9 away from each other until they come to bear against the support rollers 12 and engage over the latter by means of the cylindrical pockets 14 thereof. The cam rollers 9 are therefore located only below the respective high-lift cam, and the lever 1 follows the latter.

LIST OF REFERENCE NUMBERS

-   1) Lever -   2) Side Wall -   3) One End -   4) Other End -   5) Crossbar -   6) Gas-Exchange Valve System -   7) Bearing -   8) Axle -   9) Cam Roller -   10) First Servo Means, Hydraulic Medium -   11) Second Servo Means, Spring Means -   12) Support Roller -   13) Outer Face Cam Roller -   14) Pocket -   15) Annular Casing -   16) Outer Casing Support Roller -   17) Base -   18) Inner Face Support Roller -   19) Pressure Space -   20) Inner Face Cam Roller -   21) Annular Pocket -   22) Bottom -   23) Supply Line -   24) Transverse Channel -   25) Longitudinal Channel -   26) Annular-Groove/Bore Overflow -   27) Axial Channel -   28) Radial Passage -   29) Stop Element -   30) Center Section -   31) Intermediate Section -   32) End Section -   33) Upper Side -   34) Support Surface 

1-11. (canceled)
 12. A switchable lever for a valve drive of an internal combustion engine, comprising: an elongated housing having two side walls, one end of the housing having a crossbar for a gas-exchange valve system and another end of the housing for a bearing; an axle transverse to and fixed in the housing; two cam rollers rotatable on and concentric with the axle, the rollers transversely displaceable on the axle between a first position where the rollers abut each other and a second position where the rollers are spaced transversely apart from each other; a first means for positioning the rollers in the first position, the first means in the housing between the housing and rollers; and a second means for positioning the rollers in the second position, the second means in the housing between the rollers.
 13. The lever according to claim 12, wherein the first position provides a low-lift cam contact and the second position provides a high-lift cam contact.
 14. The lever according to claim 12, wherein each of the cam rollers have an annular casing and outer faces with pockets that have bores formed in the outer faces.
 15. The lever according to claim 14, further comprising a pair of diametrically opposite support rollers arranged on the axle, adjacent to the side walls, the support roller have an outside diameter that is smaller than an outside diameter of the cam rollers and an outer casing on which the cam rollers are at least partially mounted and an inner face opposing the cylindrical pockets of the cam rollers.
 16. The lever according to claim 15, wherein the first means is a pressure space for hydraulic medium that can be introduced via the axle, the pressure space is formed axially between the bases of the cylindrical pockets and the inner face of the support roller, which is adjacent to the cylindrical pockets.
 17. The lever according to claim 14, wherein the second means is a mechanical spring means that is clamped between the inner faces of the cam rollers.
 18. The lever according to claim 17, wherein the cam rollers can be displaced towards each other to achieve the first position, which is counter to a force of the spring means, by a high pressure of the hydraulic medium, which can be conducted into the pressure space.
 19. The lever according to claim 17, wherein the cam rollers can be displaced away from each other by a force of the spring means to achieve the second position when a high pressure at the hydraulic medium switched off.
 20. The lever according to claim 17, wherein the spring means comprises at least one helical compression spring.
 21. The lever according to claim 17, wherein the cam rollers have an inner face with opposing annular pockets, which run in a radial region above the support rollers and the opposing annular pockets have bottoms and the end sides of the spring means are supported on the bottoms of the pockets.
 22. The lever according to claim 15, further comprising an axial passage in the axle, which has at least one radial passage that branches off from the axial channel at least partially in the pressure space and is positioned axially in a region of the inner face of the support rollers.
 23. The lever according to claim 22, further comprising a supply line for the hydraulic medium having a transverse channel in the crossbar, a longitudinal channel in one of the side walls and an annular-groove/bore overflow in the axle, the supply line extends outwardly from the bearing at the second end via the transverse channel, the transverse channel opens at an outer end into the longitudinal channel, the longitudinal channel communicates with the annular-groove/bore overflow and from the annular-groove/bore overflow the supply line is conducted further to the axial channel in the axle.
 24. The lever according to claim 14, further comprising a stop element running centrally on the axle with the inner faces of cam rollers hearing against the stop element when the earn rollers are displaced into the first position.
 25. The lever according to claim 24, wherein the stop element is a snap ring.
 26. The lever according to claim 15, wherein at least one of the support rollers is slideable on the axle.
 27. The lever according to claim 12, wherein the sidewalls have an expanded center section, the center section is adjoined at each end by intermediate sections with inwardly angled contours, and the intermediate sections are adjoined by approximately rectilinear end sections.
 28. The lever according to claim 12, wherein the lever has a U-shaped pro file or upside down U-shaped profile in cross-section.
 29. The lever according to claim 12, wherein the side walls and crossbars are composed of a steel sheet or are produced by metal injection molding.
 30. The lever according to claim 12, wherein the lever is a rocker arm lever which has a dome at the second end of the bearing.
 31. The lever according to claim 12, wherein the lever is an oscillating lever which has an eye at the second end for the pivotable mounting on the axle.
 32. The lever according to claim 12, wherein the cam rollers are interchangeable or are at least substantially identical with regard to geometry and dimensioning. 